OBJECTIVES: a) To describe the effects of age and prolonged hypercholesterolemia on the canine eye. b) Goals for current year: 1) Collection of eyes (48) from group 1. 2) Ophthalmoscopic examinations during course of group 1 experiment. 3) Preparation of trypsin digested retinas from group 1 dogs. 4) Cytological examination of the digested retinas. 5) Preparation of paraffin sections of group 1 eyes. During the current year, 47 trypsin digests were completed and examined from the initial group of dogs. Statistical examination has not yet been completed. Ophthalmoscopic examinations on the animals in group 1 revealed no lesions. Studies during the first experiment, by I 131 uptake, suggested thyroid depression was inadequate. Accordingly, I131 thyroid ablation was used in addition to surgical thyroidectomy in the second group of dogs. Propylthiouracil dosage was increased from 7.5mg/kg to 40 mg/kg in gradual steps in the 2nd group in an attempt to attain higher serum cholesterol values than the first group. Control animals for I131 effect were added to the second group. Based on ophthalmoscopic examinations and the systemic vascular lesions are poor indicators of systemic vascular function. All of the goals for the current year were completed. The second group of dogs is approximately half way through the 12-month procedure. Further evaluations cannot be made until histopathology and electron microscopy are completed on both groups. The study to date, based on preliminary ophthalmoscopy data question whether the dog will be a suitable model of retinal atherosclerosis. The microscopic findings remain to be evaluated. To date no suitable animal model has been found. Research goals for the coming year: a) Statistical analysis of trypsin digest cytological data.